This invention relates to a serial digital audio data port with multiple functional configurations.
AES3-1992 prescribes a signal format for digital audio data. A signal in this format is sometimes known as an AES3 signal, or simply as an AES signal, and has two channels which may be related, for example as left and right stereo channels.
AES3-1992 specifies that the AES signal should be transmitted in balanced form over a shielded twisted pair cable. AES3-1992 specifies that in this case the cable should have a characteristic impedance of 110 ohms at frequencies from 100 kHz to 128 times the maximum frame rate, or 6.144 MHz for a frame rate of 48 kHz, that the driver should have a balanced output with an internal impedance of 110 ohms +/xe2x88x9220% over the same frequency range and that the receiver should present an essentially resistive impedance of 110 ohms +/xe2x88x9220% over the same frequency range.
SMPTE 276M-1995 describes a point-to-point coaxial cable interface for the transmission of AES digital audio signals throughout television production and broadcast facilities. In accordance with SMPTE 276M, the generator or driver must have a source impedance of 75 ohms over the frequency band 0.1 MHz to 6.0 MHz and the receiver must present an impedance of 75 ohms over the same frequency band. In a given facility, AES signals may be transmitted both in balanced form and in unbalanced form.
SMPTE 259M-1993 (hereinafter referred to simply as SMPTE 259) defines the serial digital interface (SDI) signal format for video. The SDI signal format specifies locations at which ancillary data can be accommodated in the field of a composite digital video signal or a component digital video signal.
SMPTE 272M-1994 (hereinafter referred to simply as SMPTE 272) defines the mapping of AES digital audio data into the horizontal ancillary data space of the SDI data stream, resulting in a serial data stream including both video data and audio data. The process by which AES digital audio data is inserted in the horizontal ancillary data space of the SDI data stream is referred to as embedding or multiplexing. Conversely, the process by which digital audio data is extracted from the horizontal ancillary data space of a serial data stream including both video data and audio data is referred to as disembedding or demultiplexing. See, for example, D. K. Fibush, xe2x80x9cIntegrating Digital Audio into the Serial Digital Video Signal,xe2x80x9d SMPTE JOURNAL, September 1994, 574-579 and U.S. Pat. No. 5,483,538.
Powerful digital signal processing techniques allow different configurations of a given product to perform different functions. For example, with relatively minor variations in control and software, a given functional module may be used either to embed digital audio data in a digital video data stream, according to SMPTE 272M, or to disembed digital audio data from a digital video data stream. Operating as an embedder, this module would require one or more audio inputs (as well as a video input and a video output), whereas it would require an audio output rather than an audio input when operating as a disembedder. A port that could be configured either as an audio input or as an audio output could be used to provide an audio connection to either module.
U.S. patent application Ser. No. 09/977,655 filed Oct. 12, 2001, discloses a routing switch having variable input/output configuration. This function requires that some ports should operate selectively either as input ports or output ports, depending on the required configuration.
U.S. Pat. No. 6,256,686 discloses a bidirectional serial video port.
In accordance with a first aspect of the invention there is provided a bidirectional port for digital audio data, comprising an I/O circuit including a connector having at least one signal terminal and also including a coupling circuit connected to said signal terminal and having first and second coupling circuit terminals, and a transceiver having first and second I/O terminals connected to said first and second coupling circuit terminals respectively and including a receiver having a first input terminal connected to the first I/O terminal, a second input terminal connected to the second I/O terminal, and at least one signal output terminal, a termination circuit connected between said first and second I/O terminals and including a resistor and a switch connected in series, the switch having an open state and a closed state, and a driver having at least one signal input terminal and also having first and second output terminals connected respectively to the I/O terminals of the transceiver, the driver having an enabled state and a disabled state, whereby the transceiver has multiple modes of operation depending on at least the state of the driver and the state of the switch.
In accordance with a second aspect of the invention there is provided a modular product for audio and video processing, comprising a digital video input port for receiving a digital video data stream, a processor for processing the digital video data stream and a digital audio data stream, and a digital audio transceiver for receiving or outputting the digital audio data stream, said digital audio, transceiver having first and second I/O terminals and including a receiver having a first input terminal connected to the first I/O terminal, a second input terminal connected to the second I/O terminal, and at least one signal output terminal connected to the processor, a termination circuit connected between said first and second I/O terminals and including a resistor and a switch connected in series, the switch having an open state and a closed state, and a driver having at least one signal input terminal connected to the processor and also having first and second output terminals connected respectively to the I/O terminals of the transceiver, the driver having an enabled state and a disabled state, whereby the digital audio transceiver has multiple modes of operation depending on at least the state of the driver and the state of the switch.
In accordance with a third aspect of the invention there is provided apparatus for audio and video processing, comprising a digital video input port for receiving a digital video data stream, a processor for processing the digital video data stream and a digital audio data stream, and a digital audio I/O port for receiving or outputting the digital audio data stream, the digital audio I/O port including an I/O circuit including a connector having at least one signal terminal and also including a coupling circuit connected to said signal terminal and having first and second coupling circuit terminals, and a digital audio transceiver having first and second I/O terminals connected to said first and second coupling circuit terminals respectively and including a receiver having a first input terminal connected to the first I/O terminal, a second input terminal connected to the second I/O terminal, and at least one signal output terminal connected to the processor, a termination circuit connected between said first and second I/O terminals and including a resistor and a switch connected in series, the switch having an open state and a closed state, and a driver having at least one signal input terminal connected to the processor and also having first and second output terminals connected respectively to the I/O terminals of the transceiver, the driver having an enabled state and a disabled state, whereby the digital audio transceiver has multiple modes of operation depending on at least the state of the driver and the state of the switch.
In accordance with a fourth aspect of the invention there is provided a method of making an active circuit assembly, said method comprising providing an active circuit module having an interconnection means for receiving an input signal and having an output for providing an output signal, providing a first interface module, said first interface module being a balanced interface module having two input terminals for receiving an input signal and having an interconnection means complementary to and releasably engageable with the interconnection means of the active circuit module for providing the input signal to the active circuit module, providing a second interface module, said second interface module being an unbalanced interface module having an input terminal for receiving an input signal and having an interconnection means complementary to and releasably engageable with the interconnection means of the active circuit module for providing the input signal to the active circuit module, selecting one of the first and second interface modules, and engaging the interconnection means of the selected interface module with the interconnection means of the active circuit module, whereby the selected interface module and the active circuit module are electrically connected and form the active circuit assembly, the input signal received by the selected interface module is supplied to the active circuit module, and the active circuit module provides an output signal that reflects the input signal.
In accordance with a fifth aspect of the invention there is provided a method of manufacturing an active circuit assembly, said method comprising providing an active circuit module having an input for receiving an input signal and having an interconnection means for providing an output signal, providing a first interface module, said first interface module being a balanced interface module having two output terminals for providing an output signal and having an interconnection means complementary to and releasably engageable with the interconnection means of the active circuit module for receiving the output signal provided by the active circuit module, providing a second interface module, said second interface module being an unbalanced interface module having an output terminal for providing an output signal and having an interconnection means complementary to and releasably engageable with the interconnection means of the active circuit module for receiving the output signal provided by the active circuit module, selecting one of the first and second interface modules, and engaging the interconnection means of the selected interface module with the interconnection means of the active circuit module, whereby the selected interface module and the active circuit module are electrically connected and form the active circuit assembly, the output signal provided by the active circuit module is provided to the selected interface module, and the selected interface module provides an output signal that reflects the input signal received by the active circuit module.
In accordance with a sixth aspect of the invention there is provided a bidirectional serial port for digital audio data, comprising a cable connector for coupling the port to a cable; a cable driver having a serial digital audio signal as an input and also having an output; a receiver having an input and an output; an impedance and level matching network coupled to the output of the cable driver, the input of the receiver, and the cable connector; and a means for selectively configuring the port either as an input port by causing the impedance and level matching network to act as a cable termination or as an output port by allowing the serial digital audio signal to pass through the cable driver and the impedance and level matching network to the cable connector.
In accordance with a seventh aspect of the invention there is provided a method of making a bidirectional serial port for digital audio data, said method comprising providing an active circuit including a cable driver having an input for receiving a serial digital audio signal and also having first and second output terminals, a receiver having first and second input terminals and an output, and an interface circuit connected to the first and second output terminals of the cable driver and to the first and second input terminals of the receiver and having first and second I/O terminals, providing a first passive circuit comprising a balanced cable connector and an impedance and level matching network coupled to the balanced cable connector, the impedance and level matching network of the first passive circuit having first and second I/O terminals, providing a second passive circuit comprising an unbalanced cable connector and an impedance and level matching network coupled to the unbalanced cable connector, the impedance and level matching network of the second passive circuit having at least one I/O terminal, and selecting either the first or second passive circuit and, in the event of selecting the first passive circuit, connecting the first and second I/O terminals of the impedance and level matching network of the first passive circuit to the first and second I/O terminals respectively of the interface circuit, whereby the active circuit and the first passive circuit function as a balanced port and in a first configuration of the active circuit the interface circuit and the impedance and level matching network of the first passive circuit act as a cable termination for a serial digital audio data signal in accordance with a first interconnection standard and in a second configuration of the active circuit the interface circuit and the impedance and level matching network output the serial digital audio signal to the balanced cable connector with a voltage level in accordance with the first standard, and in the event of selecting the second passive circuit, connecting the I/O terminal of the second passive circuit to one of the I/O terminals of the interface circuit, whereby the active circuit and the second passive circuit function as an unbalanced port and in a first configuration of the active circuit the interface circuit and the impedance and level matching network of the second passive circuit act as a cable termination for a serial digital audio data signal in accordance with a second interconnection standard and in a second configuration of the active circuit the interface circuit and the impedance and level matching network output the serial digital audio signal to the unbalanced cable connector with a voltage level in accordance with the second standard.